package com.qying.other;

import java.util.Arrays;

public class KMPAlgorithm {

    public static void main(String[] args) {
        String str1 = "BBC ABCDAB ABCDABCDABDE";
        String str2 = "ABCABCABDA";
        int[] next = kmpNext(str2);
        System.out.println("next = "+ Arrays.toString(next));

        int index = kmpSearch(str1, str2 , next);
        System.out.println("index = " + index);
    }

    public static int kmpSearch(String str1, String str2, int[] next){
        for (int i =0 ,j = 0; i<str1.length();i++){
            while (j > 0 && str1.charAt(i) != str2.charAt(j)){
                j = next[j-1];
            }

            if (str1.charAt(i) == str2.charAt(j)){
                j++;
            }

            if (j == str2.length()){
                return i - j + 1;
            }
        }
        return -1;
    }

    public static int[] kmpNext(String dest){
        ///"ABCABCABC"
        int[] next = new int[dest.length()];
        next[0] = 0;
        for (int i =1, j = 0; i<dest.length();i++){
            while (j>0&& dest.charAt(i) != dest.charAt(j)){
                j = next[j-1];
            }
            if (dest.charAt(i) == dest.charAt(j)){
                j++;
            }
            next[i] = j;
        }
        return next;

    }
}
